It is often desirable to have the ability to measure system variables, such as the speed of rotating elements. Many methods to measure speed are well known and many components are commercially available. One method of speed measurement is to generate an electrical signal by attaching magnets to the rotating element. A stationary pickup device, with lead wires attached to it, converts the changing magnetic flux levels into an electrical output (analog or digital) which is proportional to speed.
Some operating conditions faced by the rotating element whose speed is desired may be hostile to the attached magnetic material. For instance, in hydraulic applications, unprotected magnetic material could be subjected to high inertial forces while in an oil bath with extreme temperature variations (-40.degree. F. to 220.degree. F.), erosion from various metallic and non-metallic particles, and cavitation from entrapped air.
While magnetic speed sensing devices of various types have existed for many years, problems persist relative to the attaching of sensor magnets to the rotating element. The magnetic material attached to the rotating element is usually flexible, but is fragile, has poor mechanical properties, and cannot withstand high inertial forces. If the magnetic material is attached to the rotating element merely by adhesives, harsh operating conditions may cause the magnetic material to come loose. Although a better adhesive may prevent loosening, it may also seriously impair later removal of the magnetic material. Existing speed sensing devices are difficult and time consuming to attach and remove from the rotating element. Sometimes little clearance exists between the rotating element whose speed is desired and other stationary or moving parts around it. Although some existing devices mount directly on the rotating element, they fail to maintain a low profile while securely attaching the magnetic material and protecting it from the environment.
Therefore, it is the principal object of this invention to provide a retained magnetic strip which is fully encased within a protective ring when placed on a shaft for sensing of rotational speed.
A further object of the present invention is to provide a magnetic strip which can be frictionally pressed into a protective element as a sensing ring to measure the rotational speed of said element.
A further object of the present invention is to provide a retained magnetic strip which is easily and securely installed onto the shaft or like to be measured for rotational speed.
A further object of the present invention is to provide a retained magnetic strip which is durably protected from the abrasive effects of the operating environment around the rotating element.
A further object of the present invention is to provide a retained magnetic strip which can be pressed off of the rotating element for replacement purposes.
A further object of the present invention is to provide a retained magnetic strip which maintains a low profile above the rotating element to which it is attached.
A further object of the present invention is to provide a retained magnetic strip which is capable of withstanding high inertial forces.
A further object of the present invention is to provide a retained magnetic strip which is economical to manufacture.
These and other objects will be apparent to those skilled in the art.